Leaf Litter

Leaf Litter Talks with Ed Snodgrass

We visit Emory Knoll Farms, a nursery specializing in green roof plants, where we meet owner Ed Snodgrass, and climb on top of his office to see his own green roof.

By Amy Nelson

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Ed Snodgrass, a fifth-generation farmer and nurseryman, is president and founder of Emory Knoll Farms, Inc. and Green Roof Plants, North America’s first nursery specializing in green roof plants and horticultural consulting. Since its inception, Emory Knoll Farms has supplied plants for over 300 green roof projects throughout the United States and Canada. Ed collaborates on green roof research with academic institutions including Penn State University, North Carolina State University and Michigan State University, and he advises clients such as the Singapore Botanic Gardens and the U.S. Botanic Garden on green roof installations. A popular speaker and published author, Ed lectures widely at universities and regional, national and international conferences and has been featured in The New York Times and on the Sundance Channel’s Ecobiz documentary series, among others. Ed co-authored Green Roof Plants: A Resource and Plant Guide (Timber Press, 2006) and is currently at work on two new books for Timber Press.

When did you decide to dedicate your agricultural business to rooftop plants?

I took over the farm in 1972 and stopped farming in 1983. I made money every year, except 1982. That year, the Soviets invaded Afghanistan and we embargoed the Soviet Union, which was our biggest grain customer. This cut the price by a third. Ironically, I had my best year in 1982 in terms of yield, weather, and everything – except price. Also, at that time, interest rates were very high – 19%. So for all the money I borrowed to put my crop in I was paying back $1 out of every $5 in interest. These combined factors created a tsunami of economics, so I left farming. I came back to the farm in 1997.

I wanted to get the lexicon of “plants on top of things” out there. Since I didn’t have any green roof customers yet, I started by building little green roof birdhouses and birdfeeders and selling them at farmers markets. That got people thinking about the concept.

What sort of reaction did you get – from friends, family, members of the farming community – when you made the decision to return to farming and focus on plants for rooftops?

I was under the radar at first, because I had plants before I had customers. Sure there were some raised eyebrows. A couple of years ago, however, we won the Innovative Farmer of the Year Award, which is awarded by a peer group of farmers in the county. So obviously, I’ve gained the acceptance of local farmers.

How did your journey into sustainability begin? I read that the “The Natural Step” framework played a role. Is that true?

My father and grandfather were sustainability people for their generations. I remember getting lessons like, “Work with nature; not against it” as a little boy.

The Natural Step really gave me a framework in which to operate. It helped me make decisions when I “rebirthed” the farm from agricultural production into niche nursery.

How did you first hear about The Natural Step?

I can’t actually recall. I was Director of Education at Living Classrooms Foundation and was doing a lot of ecological, environmental and social curriculum development, and may have first run across it then. I went to Natural Step conferences in Atlanta and San Francisco. I ended up in Stockholm for something unrelated, and since I had a business card with Karl-Henrik Robèrt’s (founder of The Natural Step) address on it, I decided to find him and talk to him.

Was that the turning point for you, when you decided to go back to farming in a new way?


I didn’t leave the farm willingly. I left because I went broke. When I was off the farm, I was always trying to find a way back.

When I looked back at farming, I decided that as a businessperson, I was not controlling the revenue side of my equation because the price is set on a world commodity market. Soybeans, corn, wheat, etc. are controlled by the Chicago Board of Trade. And I wasn’t controlling the expense side of the equation. If you do row crop agriculture, you’re planting hybrid seeds, using certain chemicals, etc. If you choose to go organic, it takes you seven years to get your certification. You have to be off chemicals for seven years, so the bridge is very difficult.

We tend to have this iconic view of farmers as rugged, independent individualists. But when I looked at this from a business point of view, I discovered I was very dependent. I had no control over expense or revenue. One of the things that inspired me was to get out of that cycle of dependency and find a way that was a little more bucolic than being on a tractor in a paper suit with a respirator spraying chemicals on the land.

When you’re generational, you come into that. I also realized that the farm operation wasn’t of my design. The time away helped gestate all of that. Out of that gestation, The Natural Step became the framework to operate in. It gave me a scorecard to use. I was able to say, “If I try this crop, how does that fit in the Natural Step?”

Do you sell plants for green/living wall construction as well?


From where is most of your demand coming? How has this demand changed since you decided to focus solely on plants for roofs?

Our plants are sold in states that have evenly distributed rainfall. That goes from Georgia up through Maine, across the Great Lakes, and down through Missouri. We also have some customers in Hawaii and the Pacific Northwest. If you look at plants growing up on top of buildings without irrigation, you have to have the rainfall spread out.

Do you have any customers outside of the U.S.?

We have sold plants in Canada, Singapore, Hong Kong and Japan. But these have been more for research. The Singapore Botanic Gardens did a green roof research project. We sent starter plants to nurseries in Hong Kong and Japan. Ironically, I think a lot of the plants we sent there were Asian natives.

Has the demand for rooftop plants changed since you started this business? If so, how?

We have grown about 70% a year since 2001, from a financial point of view. The projects have increased in number and in size. The competition has increased, and we’ve still been able to increase volume, so the total market is growing.

But when your multiples are very low to start with, your percentages can be very high. I had one customer in 2000 and two in 2001, so I had 100% growth that year!

How many customers do you have now?

Hundreds. We are pushing 300 projects.

We are trying to figure out how we can ship across the whole U.S. with a very low carbon footprint. We have five or six other nurseries throughout the U.S., so we can take an order here, but fulfill it in the neighborhood where the green roof is.

Your operation is, itself, striving toward sustainability. In addition to the challenge of shipping plants throughout the U.S. while maintaining a low carbon footprint, what have been the major challenges to becoming a sustainable operation here at the farm?

Most of the technology associated with sustainability is new and unreliable. You end up doing a lot yourself, with a lot of trial and error. From a labor point of view, it’s expensive.

John Shepley, my business partner, spearheads and designs those systems for the most part. His background is in engineering. He has been steadily working through the challenges associated with some of the technologies we use.

We use alternative fuel for heating our office and greenhouses. We’ve had biodiesel gunk up some of our machinery. We’ve had vegetable oil coagulate in our boiler. When you replace fossil fuels, which have been refined and taken through the whole weights and measures and standards filter, and go instead to backyard and garage production, you get a very uneven and unreliable form. The price is low, but the quality is not consistent.

We pump all of our water with solar. That has been more reliable, but the pumps are expensive. When a pump burns up, we have to get a new one shipped from Arizona. If I had a traditional well pump go up, I’d run four miles out to the hardware store and get a new pump.

The whole alternative energy system is more disparate, unorganized and unreliable. That doesn’t mean we’d ever abandon it, but those are challenges when you’re running a commercial operation.

One of the things that is most sustainable here is what we don’t do. We grow crops that don’t need a lot of embodied energy. Most nurseries consume a great deal of energy trying to produce plants that are not easily produced in their geographic region. We limit what we grow and we keep our systems fairly simple. We don’t get a lot of off-the-shelf, expensive machines. Even for flat filling, we have a farm wagon and loose soil. It may look inefficient, but the way we measure it, we’re not buying a $65,000 flat filler and running a bunch of electricity for it. We also have a sustainable metric that goes along with a profit metric.

I read that you have dedicated a significant portion of your land to restoring indigenous trees and meadows. Is this an attempt to regenerate the landscape that was used for dairy and crop farming for so long (almost 300 years)?

I think there’s this notion that we have in the west of maximizing all of your assets all the time. We even have laws called fiduciary responsibility for corporations, where you have to maximize profit. That’s such a narrow view of what ‘profit’ means.

We have about 140 acres that my wife and I own. The family owns another couple hundred acres. We don’t have an economic reason to use every square foot of the farm. We make a pretty good living off of about 10 acres of that. Why put all that in production and have all that stuff when we can be a bit restorative? There’s another principle at work. We view things very monolithically. When you restore habitat for ground birds and have more diversity in animals and plants, you have a stronger ecosystem. It certainly could go back to agricultural production at some point. It’d be a lot easier to put a meadow back into agriculture than to put a suburb back into agriculture. You’d have to tear up septic systems, driveways, etc. I really think it’s economically viable to let it be restorative, from an ecosystem services point of view.

We are in a suburban area between Baltimore and Philadelphia. Until the downturn, the land was very valuable to sell for housing lots. I did the math in my head and said, even if our generation maximizes it by putting as many houses as we’d be legally able to put on it, the money still doesn’t last past a generation. In a generation, a million dollars goes away. But the land is producing every year, and has for generations and generations. Any generation previous to me could have sold the land and had that money in their pocket. I’m the beneficiary of their patience. So I don’t feel like it’s a light decision for me to cash out at any point either.

Has the economic gloom cast its shadow on your business?

We are still getting estimates and seeing business activity. We’re kind of a lagging indicator, though, because a lot of the projects we do are commercial or federal, so the budgets may have already been in place. I really don’t know. I think there is a bit of a green bubble. My guess is that we’ll be even or a little bit ahead of where we were last year. We are small, though. We are a six-person company, so we don’t have a lot of labor and overhead. We’re also scrappy.

What, in your opinion, is the single most important factor to consider when selecting plant material for a green roof?

The design intent and the maintenance budget. There’s way too much deciding on plants before you know what you want your roof to do and what your maintenance budget is.

For example, it seems to be intuitively obvious that you may want to use natives on green roofs because that’s an ecological system. But first you have to ask, “What is native? What concentric circles are you going to operate in?The Deer Creek Valley? The Susquehanna watershed? The East Coast?” After you define what native is, then you have to look at the conditions of that native ecosystem. This land was a mature, deciduous forest. Does that resemble the rooftop? So then you have to determine what kind of support system is needed for regional natives. In my estimation, in this area, that would mean deeper, richer soils, so you’d need to increase the loading for your building. You’d probably need irrigation. In the maintenance of your roof, you’d have to guard against succession, because as you make the system deeper, seedlings and everything else start coming in.

If someone says they want natives, I ask, “Why do you want natives?” If you drill down into the question, you get to the value. I want natives for pollinators. I want natives for bird food. I want natives for macroinvertebrates. I want natives for butterfly habitat. Then, you need to select the plants that suit that group of animals you are trying to attract. You must then understand what scale you need to create habitat, and how you treat and keep it. For example, with butterflies, if you only put up nectar plants, you’ll attract adults, and they’ll lay eggs, but there’s no larval food. The eggs hatch out and the larva will starve to death on top of the building. Larval foods are typically ugly plants and nectar plants are better looking. Everybody plants their butterfly gardens for nectar and not for larval food. This gets down in to very specific choices.

On the other hand, if you’re looking for an ecosystem service like stormwater management, you want plants that can absorb water after a drought very rapidly. You want plants that slough root systems and regrow them. If you’re looking for cooling, you want plants with a high evapotranspiration rate.

You need to look at the desired function and organize the plants according to that function.

Based on what you see with your own clients, is there one primary reason people are constructing green roofs?

In this area, most of the impetus for green roofs is stormwater management. There’s a kind of nexus between the amount of weight a building can hold and maximizing efficiency for stormwater. Obviously, if every building in a city could have a foot of soil on it, you would have almost no runoff from rooftops. But that’s an impractical financial thing to ask. It ends up being about 3 inches of media. That’s a typical profile for a green roof.

Is this true for commercial and residential buildings?

Yes, because that is around 25 pounds of load and that can be accommodated without a lot of extra expense in the construction process. Stormwater engineers have found that somewhere within that three to four-inch range, they are getting the performance they need for their system and if you spend the money to go beyond that, you have a declining curve of performance relative to cost. What stormwater engineers are looking for is to dampen the peak flow. Say you get a half inch of rain in 20 minutes. It’s not a lot of rain but fills all of the pipes in the cities and overflows. If you have that same amount of rain on a green roof, it goes off very slowly. It dampens the peak flow. A three or four-inch system will dampen the peak flow just as well as a thicker system.

Another factor is total annual volume. With three to four inches on your green roof, depending on your climate, 50-60% of annual rainfall never leaves the roof. That means if you put green roofs on enough rooftops in an urban area, you can cut in half your total volume [of stormwater] going through the system. Ninety percent of our rain events are under ¾ inch in volume. If you know these things, why build a more expensive system? At least from a stormwater management perspective.

Unless your primary goal is something other than stormwater management, such as aesthetics, increased living or recreation space and evaporative cooling, right?

Yes, but the thing about green roofs, and living systems in general, is that it’s hard for any one single thing to give you a true return on investment because emerging technologies are more expensive. But green roofs are very competitive because they do many things at the same time. You get aesthetic value, stormwater value, evaporative cooling, insulation when the system is dry, pollinator food, etc. You get all these benefits layered together.

John Todd at the University of Vermont, talks about living systems longitudinally, because they can become locally adapted to the conditions.

When he builds sewage treatments just out of biological parts. He found that after a generation or two, the plants get used to the effluent they are treating and they get better. If the system collapses, it tends to self repair. Living systems tend to self actualizing and adjusting. Mechanical systems are subject to the laws of entropy. Bearings, seize up, belts stretch, motors burn up, etc. Mechanical systems don’t adapt to variable flows very well. In a living system, if the effluent slows down, the system dampens down and goes into a stasis and can come back up as the flow increases. Treatment plants have to have a certain volume coming in at all times in order to keep all the bacteria moving.

There is a cascade of benefits on green roofs. So while you probably have a single design intent, the subsidiary benefits don’t go away. If you’re designing it for butterfly habitat, you’ll still get some carbon sequestration, evaporative cooling, aesthetic value, etc.

Have you looked at putting dollar values to the benefits for the ecosystem services provided by green roofs?

I’m on a green roof committee for LID (Low Impact Development). We have to have a long enough market to understand some of this stuff. We’re about ten years in. Roofing

membranes are supposed to last 20 years, because generally, roofing manufactures give 20-year warranties. We have a ten-year-old industry against a 20-year warranty. At the 40-year mark, we’ll know more. There’s a big economic unknown.

We also don’t have any city that has enough green roofs to have affected their stormwater infrastructure. Philadelphia needs a $2 billion pipe, Portland needs a $1.5 billion pipe Atlanta needs a big pipe. D.C. is going to need a big pipe. They have this $1-3 billion project out there and the question is, “Could you put enough green roofs up to not have to spend that?” A lot of planners are saying, “Let’s do that, because that’s going to be private sector money and not public money.” There are big returns on investment variables in the equation that are unmet.

There are some that are available that are site specific. In Portland, Oregon, there is a neighborhood development called South Waterfront that was built on a 200-acre brownfield. They did all of their stormwater management using roofs and raingardens. They needed no detention ponds at all. I believe that saved them in the neighborhood of 15 acres in detention pond that became revenue generating footprint. That pays for the green roofs right there.

Your readers should go on the City of Portland’s Bureau of Environmental Services web site and look at their green roof regulations. Chicago is doing something similar. D.C. is going to start with a different water tax rate if you have impervious area or not, which is kind of a German model. All this is changing through public policy.

At their core, cities are not getting richer. So they face this dilemma of how to provide basic services to citizens in the face of declining revenues and increasing cost.

If we go to the highest level of thinking, our city problems that are not sociological are from an imbalance of green cells vs. impervious area and animal cells. We have very high animal cells, very high impervious and very low green cells. As we raise those green cells up and get the relationship back in order, good things start happening. We don’t have as much stormwater. We have cooler cities. There are even studies showing that crimes go down around good landscaping. The University of Illinois at Urbana-Champaign has a study about this.

The German model is: if we have to spend more money because you created a bunch of impervious area, then you should participate more fully in the taxes than someone who doesn’t have any runoff. It’s like a user tax. There’s road tax in the price of gasoline. If you don’t own a car, you’re not paying for the roads to be kept up. If you own a trucking company and you’re creating more of the road wear, then you pay disproportionately high taxes. That’s where I think we’re going with city infrastructure, too.

Cities have established floor/area ratios relative to certain areas. Some cities are now saying to developers, “If you green your roofs and make your site zero discharge, we’ll give you an extra floor or three floors. It doesn’t cost the city any money. The city says to the developer, “You’re helping us with our infrastructure problem; we’ll give you more revenue.”The developer can then look at construction cost vs. revenue and make a decision. Let’s say, hypothetically, that you are a developer. Your construction cost, at the high end, is $250/square foot, including your total burden cost of your development, and you’re getting $300-$500/square foot for your property when you sell it. You can pay for a lot of green roofs and rain gardens for $200/square foot when your green roof cost might be $20/square foot. It doesn’t take much to figure out that that’s a very net positive. But not everybody is going to view it that way. You have to be able to sell the real estate.

What do you think about the feasibility of growing food on green roofs?

Everything is more trouble on a roof. The last place I’d look to grow food in the city is on a roof. It’s more dangerous. It’s windier. It’s going to dry out faster. You’re going to have to replace soil. You have issues like fall protection liability. If you look at a city like Baltimore….how many empty alleys are there? How many vacant buildings out there that could be knocked down and made into allotments? There is so much opportunity at grade, where there is water, where you can back a truck up to it, etc. It’s just a problem to do things on roofs. Maintenance is much more expensive on a roof. You’d have to have a really good reason for putting that food on a roof.

You also have to consider air quality. Some cities have horrible air quality. How much is that vegetable sequestering chromium, cadmium, mercury, lead, etc. That is all atmospheric.

The National Atmospheric Deposition Project has a web site that will show you what is at any given geographic area in terms of atmospheric deposition. If you’re downwind from a bituminous coal power plant, there’s atmospheric mercury and lead. So that’s probably not where you want to put your vegetable production. Roofs get a lot of deposition on them.

You mentioned maintenance being more expensive. Are maintenance costs generally high with green roofs?

Everything on a roof is more expensive than the corollary at grade.

How about the cost of maintaining a green roof vs. a traditional roof?

The roofing industry is a warranted industry. The warranty has replaced the maintenance. Regular roofs should be maintained two to three times a year. Flashings, drains and other items should be inspected, repaired, etc. But the owner has probably gotten a warranty from the manufacture so there is no incentive to maintain.

So it’s not an apples to apples comparison.

No, it isn’t. There’s more maintenance on a living system than an inert system. That’s for sure.

Who, in your opinion, is leading the way, in terms of doing green roofs right?

Irrespective of geography the green roof customer is someone who probably owns and operates his or her own buildings. So someone who is a speculator –who builds a building to sell it when construction is done – is generally not a green roof candidate, because it’s a bigger up front cost with benefits down the road. Generally, it’s someone who wants to own and operate his or her buildings for a long time. They tend to be more institutional clients – governments, colleges, corporate campuses. They are looking at the long term energy benefits, re-roofing costs, and possibly some kind of goodwill marketing benefit of doing a green roof.

Portland and Seattle are very concerned with stormwater. Chicago was horrified one year to have several hundred people die from heat prostration, so that got them thinking about how to cool the city in non-electrical way. A lot of tree planting, bioswales and green roof initiatives.

DC, Baltimore and New York are also incentivizing green roofs in one way or another.

So you see these cities as leading the way?

Yes, but none of them requires green roofs. Go to Lintz, Austria or Stuttgart and Frankfurt, Germany…you put up a new building in one of these cities, and it is going to have a green roof on it.

That would lead me to assume that in places where green roofs are required on flat rooftops, green roofs must greatly influence the architecture and design of new buildings. But here in the U.S., if, as you say, most speculative developers aren’t interested in green roofs, perhaps green roofs haven’t influenced architecture and engineering very much here. Is that true?

Yes, I think that’s true. But we also build differently here. Europe has the experience of having older civilizations. They build buildings to last longer, so they tend to be built heavier to start with. Their roofs tend not to need much engineering anyhow. Frankly, they have degraded their environment over a longer period of time, so they need more solutions than we may need right now. We still have a lot of very good habitat left in this country. We have a different set of problems.

Do you think rating systems like LEED are furthering green roofs?

I think it’s a double-edged sword. LEED provides incentive for green roofs, but there are LEED Gold and Platinum projects with failed green roofs. LEED might provide incentive, but it doesn’t necessarily ensure proper design, execution and maintenance.

A graduate student at Kansas State wrote a paper about LEED and Green Roofs and the concept of “chasing points.” Her paper is entitled Promoting Sustainable Green Roofs Through Leadership in Energy and Environmental Design (LEED). When you really just chase the points to get the points, there’s some voodoo there that doesn’t help with the success of the project. I think the points should be derived as a result of good, overall design. I think the LEED people would probably agree.

You mentioned failed green roofs. Have you had any “great failures” from which you’ve learned valuable lessons?

We’re not installers, but certainly we have learned a lot more about plants. We’ve had plants die. We’ve worked with designers and installers, and we have learned a lot about the weed pressure. Unlike Germany, we have warm nights. So we have a lot more weed pressure than I think many of us anticipated. We have learned that f you don’t stay on top of that in the first couple of years, you’ll see what I call “horticultural failures.” In the hierarchy green roof failures on green roofs, the most catastrophic – which I’ve never seen or heard of – is the building falls down. After structural failure, the next level of failure would be waterproofing. Then you get into the living part of failure. These are not insurmountable, but they can be pesky. If you get weeds in that produce viable seeds; if you have inappropriate plants or the wrong media, etc. After all the cranes are gone and construction is over, the costs of addressing these problems goes up.

What are some of the most common misperceptions about green roofs?

As you’d find in any emerging market, there are a lot of products and services that are untested. There’s a misperception that it’s easier than it is. One of the biggest misperceptions is that they are self-supporting systems that need no maintenance. This same thing happened about 20 years ago, when the perennial gardens were sold as low maintenance alternatives to lawn and old-style landscaping. Of course, they turned out to require just as much maintenance as any other garden. The maintenance factor has yet to rear its ugly head because the majority of roofs are under five years old.

When I asked about misperceptions, I expected the answer to be on the fear side.

On the fear side, it’s not the load, it’s the leak. People worry that their roof is going to leak.

I may have a skewed perspective because I’m on the inside. Right now there are more vendors selling green roof systems than customers. Anything that may exit you out of the sales cycle tends not to be said. Say you’re developing a new federal office building in D.C. and you want to do a green roof. You’ll have a line of roofing salespeople coming to your door. If any one of them mentioned that the roof will need aftermarket money for maintenance, I’d be surprised. That makes the project look more expensive than their portion of it. What incentive do they have to bring up the total cost when their price is just for their portion?

How do you feel about the need to educate people about maintenance?

I’m a big believer in full disclosure because I think if you’re really on top of it from the start, maintenance is not that expensive. If you don’t allow for it, then it can get very expensive.

As the concept of green roofs is relatively new in the U.S., it is no surprise that you are very involved in research and development. Can you tell us about any exciting, recent findings? Any cutting-edge techniques or materials that look promising? What about from abroad?

There’s been this notion from some of the stormwater people that we don’t really need plants on green roof, and that all you really need is the media, because that’s the sponge, and the plants don’t contribute to the system. We work with the Penn State Center for Green Roof Research. They have just proven that the plants do have a real effect on making the system more efficient for stormwater.

The other thing we are learning is that succulents evapotranspirate when water is present at about the same rate per leaf area index as corn. They are very efficient at getting water out into the atmosphere. But when the system dries up, they change their metabolism and go into survival mode. They close their stomata (pores) and can hunker down, whereas most plants continue to evapotranspirate and then sweat themselves to death.

The universities are now getting good local plant information. I think we’re a little bit away from hybridizing and breeding plants for green roofs to maximize systems.

The University of Central Florida is taking a whole other approach because it’s Florida. They are putting plants with a very high leaf index, such as bananas and calla lilies, on top of a roof. They are trying to get as much leaf area as possible. They have a pond. The stormwater goes off the roof and into the pond, and they continually pump it back up on the roof through these vascular systems.

In the cast of plant characters in the world of green roofs, is there one plant that is a star – a universally strong performer?

The genus sedum is the number one. If you took all plants off the earth and said, “Design a plant for a green roof. Here are the conditions: it has to live on existing rainfall; it can’t add weight to the structure over time; it has to be able to slough all its roots in dry periods and regrow them within a day in the presence of rain; it has to have food for pollinators.” You’d design a sedum. It has the metabolism for that. People seem to want to move beyond sedum and get into other bunches of plants, though I’m not sure why.

Perhaps for diversity?

Well, nothing’s diverse if it doesn’t live. Nothing is ecological if you have to add a bunch of plastic for irrigation and more steel for load and more embodied energy in terms of expanded materials for media. It doesn’t seem to be net ecological to deepen the soil and widen the plant palette. That’s why we always go back to design intent. If you are designing for biodiversity and aesthetics, then make that a goal, and make your building accommodate that and put a program in place to maintain that over time. I like to think of these in terms of 50-year systems. If you’re beginning with the end in mind, and you think, “I want this garden to be a 50-year garden, which I’m going to maintain two times a year,” you’re going to have a very narrow list of plants. But if you say, “I’m going to be up there every week taking care of it,” then in the same conditions, your plant list grows much wider. Again, maintenance is really a key.

There are little things you can do to remarkably change your plants. You can take a big, flat roof and put some mounds of 10-12 inches in there – possibly over columns – and you wouldn’t have a lot of extra expense. You could then put groups of plants in there that would not be sedums. But if you take sedum out entirely, you will have a failed green roof.

How early on do you generally get involved? Do you get the opportunity to ask these questions? I imagine you’re not like a typical nursery where customers come to you with a plant list.

Normal, wholesale nurseries do order fulfillment. They have an inventory, they get orders and they ship plants. When they run out of plants, they say they are sold out. We have a lot of opportunities to push back upstream into the design community. I often consult with designers. Also, if we get a list of plants we think will not lead to success, we push that information back upstream – gently. They are free to order what they originally wanted, but we feel an obligation to speak up because we care a lot about green roofs and we want them to be as successful as possible. We do see things like plants on specifications that are not hardy in that geographic region. It’s pretty easy to say, “That plant is not going to live through the winter. Is that what you intend?” The same is true if we are asked for plants that we know will be maintenance headaches. For example, if there are plants that have windborne seeds, we may say, “This is going to blow off of your roof and possibly be a problem for your neighbor.”

In researching for this issue, I have seen so many amazing examples of green roofs. What’s your favorite and why?

I think my favorite is the one above our heads because I get to see it every day. It’s just so much fun to participate in a garden every day. It’s living. It changes from day to day.

My wife and I walk a trail on the farm every day and we see something different every day. I’m very longitudinal, perhaps because my family has been here so long. I enjoy that kind of incremental, steady event, rather than the one, bright, glamorous moment. Getting to know a piece of land intimately over a lifetime is more enjoyable to me than seeing some spectacular thing for an hour. So it’s kind of in my ethos to have my favorite garden be the one I see all the time.

The roof is about three years old. It’s always evolving. It was all sedums. Then I put in some bulbs and I’ve been doing some desert annuals. So it’s evolving into something more diverse. It’s in a little design of a river, and it’s very colorful. Every three or four months, it changes color.

In your travels abroad, have you seen one standout green roofs that really blew you away?

I think my favorite was on a brewery in England called Adnams. Their business was expanding and they needed to build a new, refrigerated warehouse. They were able to eliminate all of their refrigeration units. They doubled the size of their warehouse and now, in their new warehouse, they have no refrigeration units due to their green roof and architectural features. Adnams produces the first “carbon neutral beer.” They really think about their whole supply chain.

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